Dopamine:

Colin DeYoung:

"There is this idea, that the general public seems to have, that dopamine is a pleasure chemical. Dopamine is what makes you feel good. But that's not quite right. It turns out that dopamine is what makes you want things. And sometimes wanting things feels good, especially when you think you gonna get things that you want or when you are moving toward things that are exciting or pleasurable then dopamine goes along with feeling good, but that's actually due to a whole different set of neurotransmitters[.] ... You can have dopamine without pleasure though, and that's like you really want something, but you're not getting it, and so you're feeling frustrated, and that is also dopamine. That sense 'I really need to do this. I want this.' "

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Extroversion:

"A lot of what extroversion is about is being more motivated by the possibility of reward. ... One of the ways that I like to think about dopamine: It has been described as essentially regulating the cost of effort. Doing stuff has a cost. ... Extroverts just happen to be tuned in such a way that they often think it's a good idea to expand energy. Dopamine basically gives you the signal: 'Something good could happen if you put some effort out right now.' "